If the environment variable $HOME does not exist, don't attempt to
obtain it from /etc/passwd; without $HOME, the calling process
indicates that it does not wish MPD to access the home directory.

This also prevents MPD from attempting to load
`/root/.config/mpd/mpd.conf` if MPD got started as global systemd
service.  Reading from there makes no sense, only /etc/mpd.conf shall
be used then.

This piece of code was initially added by commit 5d857921.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1687

When drop_start_samples and drop_end_samples overlap and are greater
than the actual number of samples, the `num_samples` calculation in
SubmitPCM() could underflow.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1712

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1721

For CURLINFO_CONTENT_LENGTH_DOWNLOAD_T (commit 4efd0a9f).

CURLINFO_CONTENT_LENGTH_DOWNLOAD is deprecated and is ugly because it
uses floating point.

Fix build with Boost 1.81.0. `<array>` was included by one of those boost headers,
however, it's no longer included as of Boost 1.81.0.

`master` doesn't use `std::array` in this file.

While we're at it, add all necessary inclusion files.

These settings do not work if CURL was compiled with
CURL_DISABLE_PROXY, and cause error "An unknown option was passed in
to libcurl".

Fixes regression by commit 7ab0dfc8

This compile-time option is not about debug logging, but about
curl_easy_strerror().

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1670

Of course, mode=0700 is more secure, but allowing other users access
to new directories is a choice the user should make via umask().  If
the user-chosen umask allows everybody access, MPD should probably
respect that.

This is systemd specific, and Android doesn't have systemd.

The function spl_valid_name() should verify playlist names and prevent
path traversal, but it failed to do so on Windows, because it forgot
to check for backslashes.

This buggy piece of code was already present when stored playlists
were initially implemented in 2006 by commit 08003904, and
even during the many rounds of code refactoring, nobody ever bothered
to verify it.  D'oh!

(Thanks, Paul Arzelier)

snprintf() does not return the (truncated) length actually written,
but the length that would be needed if the buffer were large enough.
This API usage mistake in FormatLastError() can lead to overflow of
the stack buffer, crashing the process (Windows only).

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1676

Fixes spurious linker errors.

If no archive library was found, return from the "plugins" directory
without creating "libarchive_plugins.a".  Empty static libraries are
unsupported on some operating systems such as macOS.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1650

Commit 44ef34db was broken.